1. Field of the Invention
The invention relates to a pressure pin with lower wear transmission of a pretensioning force to a return member in an axial piston machine.
To generate a cyclical intake and compression stroke in the individual cylinders of a cylinder drum in an axial piston machine, a swash plate is used, which, on rotation of the cylinder drum, causes the pistons in the individual cylinders to effect a cyclical reciprocating motion by means of guide shoes which are connected to the pistons and are supported on the swash plate, continuously on a circular band concentric to the axis of rotation in accordance with the rotational movement. To ensure defined support of the guide shoes on the swash plate, a pressure acting in the direction of the swash plate is exerted on the return plate carrying the individual guide shoes via a return member, which is connected with the drive shaft of the cylinder drum. To this end, the pretensioning force of a compression spring, which is guided over the drive shaft of the cylinder drum, is applied to the return member via a plurality of pressure pins.
Transmission of the pretensioning force from the compression spring via a plurality of pressure pins to the return member has caused problems in the past. Solutions in which the pressure pins are guided in separate grooves in the drive shaft require additional spring retainers for local stabilization of the pressure pins in the grooves, which complicates the assembly process and also increases unnecessarily the manufacturing costs of the axial piston machine due to the production and storage of additional components. Advanced solutions, in which the pressure pins are fixed for better guidance in grooves with limited lateral dimensions without using additional components, have the disadvantage that the pressure pins are freely rotatable against the surfaces opposite their end faces. To minimize the resultant increased wear, harder materials are required, which likewise increase unnecessarily the manufacturing costs for the axial piston machines.
2. Discussion of the Prior Art
The pressure pins in DE 198 00 631 A1 no longer exhibit the disadvantage of free rotatability relative to the surfaces adjoining the end faces (surface of the return member, surface of the spring washer), since an interference fit is provided between the pressure pins and the spring washer via a retaining hook mounted on the pressure pin in its end-face surface enlargement. A disadvantage of this embodiment, however, is that the pressure pins perform oscillating and micro-movements against the return plate. This leads to unnecessary wear to pressure pins and return plate and thus to an unintentional reduction in the pretensioning force of the return member.